Method of making a transducer diaphragm



Ja- 28 1964 M. c. sUPlTlLov 3,119,888

METHCD OF MAKING A TRANSDUCER DIAPHRAGM Original Filed July 6, 1954 i 1 am u B4-a' IN VEN TOR.

United States Patent O 3,119,888 METHOD OF MAKING A TRANSDUCER DIAPHRAGM Michael C. Supitilov, St. Charles, lll., assignor to Duirane Corporation, St. Charles, Ill., a corporation of Delaware Griginal application July 6, 1954, Ser. No. 441,335, now Patent No. 2,974,204, dated Mar. 7, 1961. Divided and this application Nov. 9, 1960, Ser. No. 68,199

2 Claims. (Cl. 264-137) This invention relates to a method of making a transducer diaphragm useful in an electrodynarnic type of microphone and/ or speaker.

In order that the invention may be fulily understood reference will now be made to the drawings wherein an exemplary method of making the diaphragm is disclosed, it being understood that variations may be made both in the construction and in the method without departing from the scope of the invention except as defined in the appended claims.

FIGURE 1 is a sectional elevation of a transducer provided With a diaphragm embodying the present invention.

FIGURE 2 is an exploded view of the various parts making up the transducer of FIGURE 1.

FIGURE 3 is a bottom View on a reduced scale along line 3-3 of FIGURE 1.

FIGURE 4 is an elevation on an enlarged scale of the diaphragm and voice coil assembly, the View being taken along broken hline 4-4 of the diaphragm of FIGURE 2.

FIGURE 5 is a sectional elevation of a die arrangement with a diaphragm disposed therein for process-ing in accordance with the invention.

The transducer assembly includes support cupof ferromagnetic material. Cup 10 has body portion 11 and annular flange supporting portion 12. Disposed within body 11 `is annular positioning member 13 of non-magnetic material and either of metal or non-metal. For example, positioning member 13 may be ott brass. Positioning member 13 has a smooth cylindrical inner surface and has two externally extending shoulders 14 and 15 and external annular bands 16, 17 and 18. Positioning member .13 has top edge 19. Band 18 has an outer diameter large enough to provide a press fit within body 11. Slidingly disposed within the bore of the non-magnetic positioning -member is cylindrical permanent magnet 2t? having magnet pole faces 21 and 22 at lthe two ends thereof. Permanent magnet is `of suitable material, such as Alnico V or other suitable material.

Permanent magnet 2d has an axial length which is greater than the axial length of positioning member I13. When permanent magnet 2t) is disposed Within the bore of positioning member 13 and the positioning member pressed into body 11, one pole of the magnet may contact the bottom of the cup body while the other pole of the magnet can extend above the level of free edge 19 of the non-magnetic lpositioning member. It is understood, of course, that the two end faces of the permanent magnet are ground to `a smooth nish.

Ferromagnetic pole piece 25 is provided for covering and contacting the :free pole face of the permanent magnet. Pole piece 25 has annular portion 26 extending around band portion 16 of the non-magnetic positioning member. The outside diameter of pole piece 25 is smaller than the inside diameter of body portion 11 of the support cup to form annular air gap 27. Pole piece Z5 has its outer surface 28 curved convexly as shown, central portion 29 being concave. Pole piece 25 makes intimate contact with the free face of the permanent magnet.

At this point, it might be observed that pole piece 25 preferably has a tight press fit over band 16 of positioning ICC member 13. Magnet 20, however, can easily lit within member `13 `and thus variations in magnet size will be accommodated. When pole piece 25 is fitted over positioning member 15, the parts may be assembled by forcing member 13 into body portion 11. Positioning member 13 will -be forced into body portion 11 deep enough so that the permanent magnet is caught between the cup bottom and the inside surface of the pole piece. The assembly is thus tightly retained in such relation.

Resting upon annular flange portion 12 is a diaphragm generally indicated by 33. The diaphragm consists of annular support portion 34, roll 34a, voice coil bobbin support part 34h, and dome 36, 'Ihe fabricated diaphragm has cemented thereto at 34h Voice coii bobbin 35. Voice coil bobbin 35' carries voice -coil 37 of conventional construction, insulated leads 38 of fthe voice coil being attached to annular support portion 34 and extending out through suitable apertures 39 in the cup flange for connection to the outside. Voice coil bobbin 35 and voice coil 37 operate in annular air gap 27. The diaphragm may be made of suitable material, such as cotton, silk, nylon, plastic, or any other material as paper. When a porous material is used for the diaphragm, it may be impregnated with a suitable thermosetting plastic compound, such as for example Bakelite resin. The resin functions to stiften the diaphragm, waterproof the same, close the pores and strengthen the material. The diaphragm treatment will be given later. The voice coil bobbin may be of porous or non-porous material. The voice coil and cemented region at 34h render the bobbin non-porous.

The diaphragm is mounted so that annular support portion 34 lies on flange part 12 of the cup. Gasket 40 is disposed at the rim of lthe diaphragm and within ferrule 41 ofthe flange. Thereafter, conventional fine and coarse screens 42 and 43 are disposed in position for completing the construction. Coarse screen 43 has its edge curled under the flange. Coarse screen 43 is strong enough so that the microphone is protected against damage while fine screen 42 keeps dirt and dust out.

In accordance with this invention, the diaphragm is divided into two separate areas which are respectively porous or open to permit air to pass through, and nonporous or closed to air. Where a diaphragm is made of a material such as, for example, woven material which is normally porous, it is possible to utilize one feature of the present invention and fabricate the diaphragm to obtain the desired porous and non-porous diaphragm parts. Thus the woven material may be dipped into or have a thin solution of a thermosetting plastic resin applied thereto. The fabric may have a thickness of several thousandths of an inch, say about .0G The coated fabric is then subjected to heat and pressure between two complementarily shaped dies to provide the desired shape of diaphragm. This procedure so far is old and widely used. Thus loud speaker spiders are manufactured in this fashion. However, and in accordance with this invention, the complementarily shaped dies have the clearances between the opposed parts abnormally large where the diaphragm material is to be porous. Thus with normal die clearances, the diaphragm material may have its thickness reduced to less than one-half of the original thickness of the Woven material at those regions where the diaphragm is to be non-porous. Under the heat and pressure at these regions of normal die clearance, the plastic resin is forced into the pores of the woven material. Where the die clearance is abnormally large, the pressure will be below the value for compressing the Woven material and squeezing the resin into the pores. It is understood that the transition from the parts of the dies having normal clearance to the parts of the dies having abnormally large clearances may be gradual if desired. This will result in a gradual change of porosity of the diaphragm material from porous to non-porous.

It is clear that there are various degrees of porosity. The advantage of the new diaphragm is that the nonporous part which may be considered as the variable factor is restricted to an area which is substantially less than the area of the entire diaphragm. Hence variations in porosity of the porous part in a diaphragm embodying the present invention will have much less eiiect than the same variation in a diaphragm having its entire area of the same unit porosity.

Inasmuch as part 34 of the diaphragm is clamped and rests upon an imperforate metal surface, it will be clear that whether part 34 is porous or non-porous is immaterial. For the purposes at hand, it is easier to fabricate the diaphragm so that roll 34a and annular part 34 are both porous.

Referring for example to FIGURE 5, anvil 45 and die 46 have suitable complemental shaped surfaces 47 and 48 for hot pressing diaphragm 33 to the required contour. Voice `coil support 35 has not been cemented to the diaphragm as yet. Anvil part 45 may have electric heater 50 within the body, threaded insert 51 permitting introduction of the heater Within the anvil body. Any other disposition of heaters is possible, the die construction being conventional except for the clearances between the die and anvil. It is understood that die 46 is carried by a ram so that the diaphragm blank may be subjected to a hot press operation.

In this instance it is desired to have dome 36 nonporous and roll 34a porous. As will be evident, the line of demarcation between the porous and non-porous parts of the `diaphragm as a whole may be placed at any desired part of the diaphragm. As indicated in FIGURE 5, the simple sectioning 52 indicates normal die clearance while sectioning 53 indicates larger than normal die clearance.

By normal die clearance is meant a die clearance which will force the impregnating resin into the pores of the diaphragm material under operating conditions of pressure and temperature. No amount of die clearance can be stated as normal since that depends on die pressure and diaphragm material. However, by having certain parts of the die clearance larger than normal, then the porous diaphragm part will result. As a rule, the larger than normal die clearance may vary. Thus the die clearance `may be enlarged from about 25% to over 100%, depending upon die pressure used, nature of the resin and temperature. The die clearance change need not necessarily be symmetrical around the diaphragm, al though this will be the simplest and easiest construction of the dies.

Depending upon the nature of diaphragm stock, the nature of resin and desired die pressure and temperature, a large variety of diaphragm patterns of porous and nonporous regions is possible.

In the diaphragm illustrated in the drawing, the porous part, for practical purposes, is confined to roll 34a. As has been previously pointed out, part 34b, to which the voice coil bobbin is cemented, is rendered non-porous by virtue of the presence of the inner layer of material of which the bobbin is made. As a rule, voice coil bobbins are of kraft paper or may be of plastic or the like.

With dome 36 of the diaphragm non-porous and roll v 34a porous, a path for air around the diaphragm will be established when the transducer is assembled as illustrated in FIGURE 1. Thus referring to this ligure, air from outside of dome 36 may pass through the porous portion 34a into annular air gap 27, around the bottom edge of the voice coil bobbin and thence inside the voice coil bobbin to the inside surface the diaphragm. Such an air path contains resistance determined by the dimensions of the clearances on the outside and inside of the voice coil and bobbin within the air gap. As a rule, efliciency requirements make it advisable to reduce the air gap to a minimum size. In practice, therefore, the shunt air path described above is eifectivewprincipally for low frequencies. If desired, however, one or more fine apertures may be provided in the voice coil bobbin and support part 34b to provide additional shunt air paths.` Thus for example, it is possible to have diaphragm dome 36, now shown as non-porous, porous over part or all of its area and roll 34a and annular part 34, now shown as porous, nonporous in part or in whole.

It will thus be evident that a very large range of transducer operating characteristics may be obtained by having diaphragm dome 36 porous or non-porous, in whole or in part, annular part 34a porous or non-porous, in whole or in part, and/or providing air relief ports through diaphragm part 34h and the underlying area of voice coil bobbin. In practice, however, a large range of transducer characteristics may be obtained by having the diaphragm constructed with regard to porous or non-porous portions as illustrated in the drawing and simply making the diaphragm material and the closeness of the weave or porosity thereof as the variable.

Where the diaphragm is of naturally non-porous material as plastic or metal, then ports asdescribed above Will be desirable.

In order to control the area of porosity in the diaphragm without changing the molding dies, a control of the molding pressure as well as controlling the thickness of the diaphragm material and the nature of the plastic used for molding will all be useful. 'Ihus the closeness of the weave of the diaphragm material, the nature of the diaphragm material such as, for example, whether the material is linen, nylon, or other textile fibers, the size of the iibers used in making the diaphragm and the nature of the molding material used may all be readily controlled and varied to obtain desired results with the same set of dies. The die pressure may also be varied. Thus one set of dies may be used for obtaining a wide variety of diaphragms in order to obtain a wide variety of frequency response characteristics.

In the drawing the diaphragm dome is shown as provided with aA concave center portion. The pole piece is also concave at the center to clear the diaphragm. These may be omitted if desired.

It is clear that the invention provides a method for constructing an acoustic diaphragm from a normally porous flexible material. This method provides for impregnating the normally porous iiexible material with a fusible thermosetting resin and shaping such impregnated material by moulding and curing in the manner disclosed. This particular manner involves moulding and curing a central projecting portion which is non-planiform, this being accomplishedat a temperature and pressure sutlicient to cause the resin to ow and to cure so that said resin can attain an infusible state. The peripheral diaphragm portion which for diaphragm purposes must remain exible, has the resin cured at a temperature and pressure below that at which the resin will ow. Thus the peripheral portion does not have the resin filling th e pores and consequently the peripheral portion retains its porosity and exibility. t

This application is a division of my application Serial No. 441,335 filedJuly 6, 1954, now Patent No. 2,974,204, issued March 7, 1961.

What is claimed is:

1. A method for constructing an acoustic diaphragm which comprises impregnating a normally porous flexible material with a fusible thermosetting resin, shaping said impregnated material by molding and curing a central non-planiform projecting portion at a temperature and pressure suflicient to cause said resin to ilow and to curse said resin to its infusible state, and curing the resin on a peripheral exible portion at a temperature and pressure below that at which the resin will ow.

2. A method for constructing an acoustic diaphragm References Cited in the file of this patent which comprises iinpregnating a normally porous flexible UNITED STATES PATENTS material with a fusible thermosetting resin, shaping said impregnated material by molding and curing a central bgg/2g non-planiform projecting portion at a temperature and 5 2:425004 Raben Augz51947 pressure suicient to cause said resin to ow and to cure 2,432,993 Jennings Dec. 23, 1947 said resin to its infusible state, and simultaneously em- 2690820 Raes OGL 5, 1954 bossing and curing the resin on a peripheral flexible por- 2,819,209 Pall et al lan. 7, 1958 tion at a temperature and pressure below that at which 10 2,850,559 Stickel Sept. 2, 1958 the resin will ow. 2,963,744 Cooper Dec. 13, 196() 

1. A METHOD FOR CONSTRUCTING AN ACOUSTIC DIAPHRAGM WHICH COMPRISES IMPREGNATING A NORMALLY POROUS FLEXIBLE MATERIAL WITH A FUSIBLE THERMOSETTING RESIN, SHAPING SAID IMPREGNATED MATERIAL BY MOLDING AND CURING A CENTRAL NON-PLANIFORM PROJECTING PORTION AT A TEMPERATURE AND PRESSURE SUFFICIENT TO CAUSE SAID RESIN TO FLOW AND TO CURSE SAID RESIN TO ITS INFUSIBLE STATE, AND CURING THE RESIN ON A PERIPHERAL FLEXIBLE PORTION AT A TEMPERATURE AND PRESSURE BELOW THAT AT WHICH THE RESIN WILL FLOW. 